My 20-month old has learned many words to express herself. In addition she says many other words that are indecipherable from context nor pronunciation. It's most noticeable in novel or unusual situations.
Is she inventing words to express the new or not-yet-learned situation? If so, (until she learns the "correct" word), will she continue to use the invented word for a while, or will she invent a different word should the situation recur? What does the literature in developmental psychology have to say about this?